1. Field of the Invention
The present invention relates generally to ovens and, more specifically, to a rotational molding oven able to be operated in a bi-axial rotational mode, a rock and roll mode or both, wherein the mold is both heated and cooled evenly by the oven with resin evenly distributed throughout to manufacture a primarily hollow or a partial shell object.
2. Description of the Prior Art
Numerous types of ovens as well as numerous methods and apparatus for forming an object have been disclosed in the prior art. One such example of a method used for forming an object is rotational molding. Rotational molding is a method of manufacture for forming primarily hollow or partial shaped plastic objects. This process utilizes a shell mold having a cavity bounded on five sides by the mold. The sixth side of the cavity is formed by a cover attached by clamps or bolts to one of the adjacent sides. When the cover to the mold is open, a powdered (possibly colored) plastic resin is placed into the cavity of the mold. The cover is then sealed to restrict access to the cavity and the mold is placed in a heated environment in which it is rotated about two axes. The heat causes the resin to melt against the inside surface of the mold. The melted resin flows within the cavity to form a viscous membrane conforming to the mold""s inner surface. The mold (and the plastic inside) is then cooled while rotation continues causing the resin to harden in the shape of the cavity filled thereby.
When the hardened resin is cool enough to handle (normally below 150xc2x0 F.) the rotation is stopped and the mold opened. The hardened resin forming a desired part is removed. The part is then trimmed and cut to the desired final contour(s) for the part. These parts are generally of uniform wall thickness, colored throughout, and unstressed, (i.e. the parts will not deform if subject to cyclical heat or heating/cooling).
Rotation can be either complete revolutions about two axes or complete revolutions about a primary axis (y) with partial revolutions about a secondary axis (x). The latter motion is called xe2x80x9crock and rollxe2x80x9d as the partial revolutions look somewhat like a cradle being rocked. In both cases, the two axes of rotation are mutually perpendicular, rotation about the vertical axis (relative to the mold centerline when the centerline is horizontal) is not required.
The quality of the part produced is heavily dependant upon motion controls exercised during both the heating cycle and the cooling cycle. The progress of the mold through the heated cavity must distribute the resin evenly and at the same time expose the surfaces of the mold to the oven heat in a uniform manner regardless of the irregularity of the surface. Therefore the motion must be configured to the specific mold and be subject to total control.
For most ovens the rotations are at a fixed rate. This provides for all exposed sides to be treated equally. The direction of rotation is also fixed for several cycles between reversals. In bi-axial, turret and shuttle machines it is possible to slow down or speed up the rotation but not reverse it in mid cycle. In rock and roll machines some angles of rotation are out of range. The present invention overcomes these limitations by providing a controlled rotation with mid revolution pause, reversal or speed change for the second axis (the x axis) and reversal and speed change for the primary axis (the y axis). It is possible to simulate either a bi-axial oven or a rock and roll oven by setting suitable limits. It is also possible to create a more complex rotational pattern by using multiple stop-start and speed change options.
Furthermore, U.S. Pat. Nos. 5,705,200; 5,807,589; 5,554,394; 5,507,632; 5,116,213; 5,039,297; 4,836,963; 4,632,654; 4,583,932; 4,102,624; 4,022,564; 3,938,928; 4,486,172; 4,767,321; 5,423,248; 5,683,240; 5,443,382; 3,914,105; 3,885,016; 3,841,821; 3,825,395; 3,822,980; 3,810,727; 3,796,533; and 3,703,348 all are illustrative of such prior art. While these units may be suitable for the particular purpose to which they address, they would not be as suitable for the purposes of the present invention as heretofore described.
A method of continuously forming an integrally molded structure in a multiaxis rotational molding operation includes the steps of rotating a multisection mold assembly about at least three axes. A first freshly formed polymerizable mixture is flowed over surfaces of an enclosed mold cavity within the multisection mold assembly. The flowing of the first mixture over the mold cavity surfaces and formation of a first resin therefrom is monitored. A second freshly formed polymerizable mixture is flowed under pressure through an orifice into the mold cavity. A liquid stream of the second mixture is formed. The liquid stream is gelled as it advances through the mold cavity to form a continuous filament with structural integrity. The filament is contacted with the first resin formed within the mold cavity. The filament is distributed over the first resin in a preselected pattern. A third freshly formed polymerizable mixture is flowed over the filament pattern formed within the mold cavity with the second mixture. The flowing of the third mixture and formation of a third resin therefrom is monitored. The rotation of the multisection mold assembly is continued throughout the steps of the continuous molding operation while monitoring individually each axis rotation of the multisection mold assembly. The monitored flowing of each mixture and the monitored formation of each resin with each monitored axis rotation is coordinated in a preselected profile to form the integrally molded structure of the first, second and third resins. Also, apparatus forming the structure is included.
A screw with replaceable threads is particularly useful to releasably join the spiders of rotational molding machines. The screw comprises a master bolt that passes through a first spider, and a tip that is removably assembled to the master bolt. The tip is threaded to selectively engage and disengage a receiver on the second spider. When the tip is assembled to the master bolt, the screw is captured in the first spider. When the tip has worn through use, it can be replaced without disturbing the master bolt. Similarly, when the tip seizes to the receiver, the tip and receiver are replaceable as a unit without disturbing the master bolt.
A molding apparatus is provided which consists of three frames which are relatively pivotal with respect to one another. One frame (A) is cradled in a second frame (B) and provision is made for tilting the first frame relative to the frame in which it is cradled. The cradling frame and the frame cradled therein are made tiltable relative to third frame (C). The tilting operations are effected by hydraulic piston and cylinder arrangements (170, 176). The method of the invention consists of cradling the first frame in a second frame, tilting the first frame relative to the second frame to a certain angle of inclination and thereafter tilting the cradling second frame along with the cradled first frame therein to a second angle of inclination relative to the third frame.
Multi-axis rotational molding apparatus includes a support portion, a molding portion, a mixing portion and a control portion. The support portion includes an arm member disposed in a generally horizontal orientation and having one end extending from an upstanding supporting section. The molding portion includes a mold supporting assembly pivotally connected to a free end of the arm member and an independently rotatable mold connector section. The mold supporting assembly includes a central passage therethrough from a pivotal connection with the arm member and through the mold connector section. A mold assembly includes at least two separable mold sections forming a substantially enclosed cavity. The mixing portion includes an elongated section extending axially within the central passage through the mold supporting assembly adjacent the mold connector section. The mixing section includes a plurality of deflector sections disposed along the length thereof. A plurality of inlet conduits extends along the arm member and is operatively connected to an inlet end of the mixing section. A hollow probe member extends from an outlet end of the mixing section into the cavity of the mold assembly. The control portion includes actuators rotating the mold connector section and the mold assembly affixed thereto and actuators pivoting the mold supporting assembly and the mold assembly affixed thereto with respect to the arm member, a programmable memory, a coordinator, monitors and circuitry.
Apparatus for selectively rotationally molding an industrial drum in either a closed-head configuration or an open-head configuration within a mold constructed for selective modification to accomplish molding of the drum in either selected configuration by inserting or deleting a separator between a first mold cavity for forming the body of the drum and a further mold cavity for forming the head of the drum, the further mold cavity being selected from alternate second and third mold cavities, such that both the body and the head are rotationally molded simultaneously within the mold during molding of either configuration of the industrial drum.
Rotational molding apparatus for molding a kayak and the like in a mold (12). The apparatus includes an oven (A) having an oven chamber (40). A frame (B) pivotally supports oven (A) above a ground floor (10). Mold (12) rotates about a roll axis (123) on a carriage (C) while in oven chamber (40). Oven (A) pivots about a pivot axis (72) in counter-pivotal movement. Oven pivot axis (72) is spaced a distance xe2x80x9cdxe2x80x9d from roll axis (123) of mold (12). This causes a pendular motion to be imparted to the mold (12). Mold (12) thus swings to and fro in an arc as oven (A) pivots. Mold (12) rotates about its roll axis (123) at the same time. A well-controlled, even distribution of plastic material in the mold occurs by this combination of motions. A desired pattern of heat distribution is applied along the length of mold (12) by a series of hot air openings (50a-50d) and a like number of openings on an opposing side of a hot air plenum (49).
An improved rotational molding method for making a laminated plastic structure of the type in which successive charges of particulate plastics are released in a mold cavity rotating in an oven to coalesce successively along the mold cavity wall after which the mold is removed from the oven for cooling. By removing the rotating mold from the oven prior to completion of the formation of the inside layer, cooling of the outside of the mold will be concurrent with coalescence of the inside layer. This shortens the time of the molding cycle and reduces warping problems.
Rotational molding apparatus and methods for rotationally molding castable material such as polymers and other materials. In one form, a shuttle or wheeled carriage containing a mold fixture for holding one or more molds, which fixture is both pivotable and rotatable on the carriage, is operable to move along a fixed path into and out of an oven and a cooling chamber. Two of such mold fixture containing carriages may be automatically moved between the oven and one or more cooling chambers, alternately to permit the oven and cooling chamber or chambers to be operated substantially all of the time during an operating shift. An automatic programming device or computer operates to control the movement of the carriage or carriages into and out of the oven and cooling chamber, the operations of the fixture rotating and pivoting motors and, if utilized, the operation of automatic mold charging equipment, the cooling chamber water pumps, the oven heating elements, mold opening and closing means, molded article removal equipment, etc. In a particular form, mold containing carriages alternately move into the oven and cooling chamber along a single track wherein one carriage is either sidetracked or moved to the side of the single track while the other carriage travels between the oven and cooling chamber.
A rotational moulding machine comprising a heat-insulated enclosure mounted to rotate on a frame about a substantially horizontal axis, which enclosure comprises means for receiving and driving in rotation at least one mould about an axis perpendicular to the axis of rotation of the enclosure, wherein said enclosure further comprises, inside, radiating elements located in front of the walls of the enclosure whose radiations are reflected by reflector means towards the central part of the enclosure where the mould is located in order to heat said mould by radiation.
An apparatus and process is disclosed for rotational molding. Rotational molding is a technique for the fabrication of parts from powdered thermoplastic material in which the thermoplastic material is placed within a hollow mold and the mold is rotated in a heated environment until the thermoplastic material fuses and coats the entire interior surface of the mold. Included in the apparatus is a holding mechanism for the mold and a power mechanism to provide the required rotational motion to the mold. The power mechanism provides for simultaneous rotation of the mold about two orthogonal axes and is displaced spatially from the holding mechanism. The holding mechanism is attached to a translating mechanism which positions the molds both internal to and external to a heating chamber such as an oven while keeping the drive mechanism external of the oven at all times. More specifically there is disclosed an apparatus which includes a truck mounted upon a guiding track and having extending therefrom an arm mechanism. The arm is pivotally attached to the truck and is coupled thereto in such a manner that the arm may be translated about the pivotal point through a vertical path from a horizontal position at a loading/unloading (mold rework) station through approximately 180xc2x0 to be positioned into a heating chamber at a heating station and a cooling chamber or tower at a cooling station for fabrication of the molded part. Subsequently, thereto the mold attached to the arm may be repositioned at the mold rework station for the removal of the plastic part from the mold. Automatic control mechanisms and interlocks are provided to enable safety measures to be exercised to prevent movement of the truck along the track except at specified times and when the arm is in appropriate position to clear the oven and cooling towers.
A molding apparatus which is provided with a frame including a bar acting as a mold support. The bar is pivoted between two angular limits and carries a gear wheel to be pivoted therewith. Planetary gears are engaged with the gear wheel and are displaced pivotally around the gear wheel to be rotated by the same. Molds are coupled to the planetary gears to be rotated therewith. Heating devices are located below the molds to heat the molds as they are being rotated simultaneously about their axes and about the axis of the gear wheel.
A rotary casting apparatus for molding hollow articles of synthetic plastic is described employing a plurality of hollow molds which are heated and rotated within a fixed oven. The molds and molded articles therein are cooled rapidly while they remain within the oven by injecting cool, moist air into such oven from an external blower fan and a sprayer which sprays water into the air inlet of such fan. Improved rotation and support means are provided for the molds, including a common tubular drive shaft which rotates all of the molds about a common axis and a plurality of rotor means for rotating each of the molds about another axis perpendicular to such common axis. The rotor means are coupled by bevel gears to a second drive shaft extending through the common drive shaft. Each of the molds is rotationally mounted on bearings which are supported on the common drive shaft. The bearings at the inner ends of the molds each include a tubular fixed shaft about which the mold is rotated by the rotor means and which also vents gas from such mold. A scraper ring of low adhesion material is attached to the fixed bearing shaft within each mold and spaced a predetermined distance from its inner surface to provide the molded article with a mounting flange portion of predetermined thickness and inner diameter.
The present invention is an oven and method of operation for heating thermoplastic articles. Articles are fed into the oven on a conveyor belt. There is a heating plate directly beneath the article bearing surface of the conveyor belt which heats the supported side of the article. The surface of the article not in contact with the belt is heated by conventional means within the oven.
A method and apparatus for heating fibers reinforced thermoplastic sheets is disclosed. The apparatus involves use of gas heating ovens adapted to allow several layers of material to be heated continuously, with the conveyors stacked are above the other. Stacking of the heated product can be provided at the oven exit. Provisions for cleaning and diffusing the gases over the work piece are also described.
A method and apparatus for heating a product which includes a plurality of tapered ducts in a cabinet above and below a conveyor to form streams which are directed toward the product. Spent air is drawn through return ducts which have intake openings centered between entrance and exit openings in the cabinet and centered between lateral edges of a conveyor and between the tapered ducts to provide a balanced flow of spent air in the cabinet to the return opening. Temperature controlled gas is delivered at an angle through an array of openings adjacent opposite edges of an opening through which a conveyor extends to cause most of the heated air to be drawn to the return duct opening and to maintain internal pressure in the cabinet to prevent ingress and egress of air through the opening.
A method and apparatus for heating a product which includes a plurality of tapered ducts in a cabinet above and below a conveyor to form streams which are directed toward the product. Spent air is drawn through return ducts which have intake openings centered between entrance and exit openings in the cabinet and centered between lateral edges of a conveyor and between the tapered ducts to provide a balanced flow of spent air in the cabinet to the return opening. Temperature controlled gas is delivered at an angle through an array of openings adjacent opposite edges of an opening through which a conveyor extends to cause most of the heated air to be drawn to the return duct opening and to maintain internal pressure in the cabinet to prevent ingress and egress of air through the opening.
An atmospheric oven containing an atmospheric gas kept at a predetermined purity accommodates a transport for transporting an object to be heated along a predetermined transporting path. A rectangular sectioned tubular body for preventing the gas from flowing outside the oven extends a certain length from an entrance of the oven Sand an exit of the oven and has a sectional area necessary for passing the object through the tubular body.
Apparatus is provided for the molding of a hollow article from a thermoplastic material. This apparatus includes a hollow mold including first and second complementary mold parts having a common axis of rotation. The mold parts are provided with engageable edges at which the parts abut to seal the mold against the leakage of the thermoplastic material. These engageable edges may take the form of flanges which are perpendicular to the axis of rotation of the mold. A rotation mechanism is provided to support one of the parts and to rotate the same on the axis of rotation. A releasable clamp is provided to clamp the other of the two parts releasably against the rotated part such that the two parts rotate together when the clamp is effecting a clamping force thereon.
The process of the invention is provided for molding hollow articles from thermoplastic materials. The process comprises depositing a measured amount of thermoplastic material in a hollow metal mold having a side and bottom walls and rotating this mold about a horizontal axis while simultaneously heating the mold during its rotation until a layer of partially fused material is formed against the side wall thereof. The mold is then pivoted to an attitude which is inclined approximately forty-five degrees to the horizontal and the mold is heated in this attitude for an additional period of time until a layer of partially fused material is formed against the bottom wall. The heating of the mold is continued until at least substantially all the material is fused, whereafter the mold is cooled and the thusly molded article is removed from the mold. The article of the invention is an open container prepared in accordance with the aforegoing method.
A technique is provided for molding a plurality of pan-shaped plastic articles simultaneously. This is done by arranging open pan-shaped molds coaxially along an inclined axis with a rectangular frame supported on shafts inclined at about 45xc2x0. Plastic poured into the individual molds is fused by a burner arranged below the frame and parallel to said axis.
Apparatus for molding hollow plastic articles in which a mold is simultaneously rotated about two mutually perpendicular axes, a source of heat being located at a position generally radially displaced relative to a circle described by the mold. The mold is supported in a frame which is of adjustable size, there being provided a telescopic drive for rotating the mold and which is extensible to accommodate adjustments in the frame.
Rotational molding apparatus including a mold-carrying frame which is mounted on a track for movement between a mold-working station and an oven. The oven is rotatable under power about a substantially horizontal axis and has a door on one of its sides. With the oven in one position, the door faces toward the mold-working station. The mold-carrying frame may be moved along the track and directly into or out of the oven through the doorway. With the door closed a substantially totally enclosed chamber is provided in the oven. Ducts in the oven are operable to circulate heated air about a mold rotated in the oven. The oven and mold frame may be rotated about the oven axis in either of reverse directions. The mold frame also is adapted to be rotated within the oven in either of reverse directions about an axis disposed at a substantial angle to the oven axis. The mold-working station includes an enclosure having a movable top which may be moved between a position overlying the mold in the station and a position where it is spaced laterally of the mold.
Apparatus for molding hollow plastic articles in which a mold is simultaneously rotated about two mutually perpendicular axes, a source of heat being located at a position generally radially displaced relative to a circle described by the mold. The mold is supported in a frame which is of adjustable size, there being provided a telescopic drive for rotating the mold and which is extensible to accommodate adjustments in the frame. In the above-indicated apparatus as well as apparatus of the same type, the mold will generally have a profile such that the relative spacing between the mold and source of heat will vary during relative movement therebetween. To provide thermal compensation for the tendency of the relative spacing to change, there is provided a cam rotatable with the mold and having a profile corresponding with the profile of the mold which controls either the flame of the burner constituting the source of heat or the physical location of the burner relative to the mold or both. The control is effected through a series of servo mechanisms controlled by a cam follower.
A rotary molding machine for producing articles of plastic which comprises at least one rotary frame of a shape similar to that of a so-called gyrowheel or Rhonwheel which is driven about a horizontal main axis and is supported on rollers and in which a table or the like is rotatably mounted on which a mold is to be supported and which together with the mold is driven about an axis extending transversely to the main axis. By employing such a rotary frame, it is possible to mount molds on the rotary frame which far exceed the dimensions of the molds which could previously be employed in rotary molding machines for producing plastic articles.
Apparatus is provided for molding thermoplastic articles in hollow form in which a frame or stand is provided which has two stable positions. These are selectively employed to hold a mold in inclined or horizontal attitudes, the mold being provided with an open end on which is placed a cover with an opening therein so that access to the interior of the mold is possible. Thermoplastic material is placed in the mold which is heated so that the material fuses to the mold and the article is thereby formed. Access to the interior of the mold permits improved control over the formation of the objects being molded and permits various possibilities such as forming articles with stripes therein or with mechanical parts incorporated into the object.
The present invention relates generally to ovens and, more specifically, to a rotational molding oven able to be operated in a bi-axial rotational mode, a rock and roll mode or both, wherein the mold is both heated and cooled evenly by the oven with resin evenly distributed throughout to manufacture a primarily hollow or a partial shell object.
A primary object of the present invention is to provide a rotational molding oven that will overcome the shortcomings of prior art devices.
Another object of the present invention is to provide a rotational molding oven which is able to operate in either bi-axial or rock and roll modes or both to optimize the quality control of a molded product.
A further object of the present invention is to provide a rotational molding oven which is able to both heat and cool the molds positioned within a cavity thereof wherein all cycles begin from the same start-up state with the same preheat cycle thus providing consistent mechanical and thermal cycles which reduce the part-to-part variance and number of rejects produced.
A yet further object of the present invention is to provide a rotational molding oven wherein the sequence and speed of rotation of the mold can be controlled to suit the particular object being formed.
A still further object of the present invention is to provide a rotational molding oven including drive assemblies for both a primary and secondary axis of rotation located completely outside the cavity to facilitate maintenance on the oven and minimize exposure of the drive assemblies to extreme temperature and humidity environments such as that found within the cavity of the oven, wherein drive trains connect the drive assemblies with their respective shafts, the drive trains being entirely contained outside of the heated cavity.
An even further object of the present invention is to provide a rotational molding oven wherein the burner combustion chamber, which may be located external and below or to the rear of the oven, is capable of operating on a variety of fuels and provides hot gasses to a plenum located below the cavity.
A still further object of the present invention is to provide a rotational molding oven including an exhaust stack having a volume control damper for controlling cavity pressure and a re-circulating fan connected to the cavity and discharging through the combustion chamber to increase gas recirculation velocity, to optimize combustion and to reduce tramp air infiltration into the cavity.
A yet further object of the present invention is to provide a rotational molding oven having a cavity generally comprised of an insulated spool operating within an insulated stationary shell, wherein the sides of the spool act as the side walls of the cavity and which spool is itself rotated to provide the secondary axis of rotation.
A still further object of the present invention is to provide a rotational molding oven wherein the drive train for the primary axis drives a sprocket acting at the center of the secondary axis, rotational motion of the sprocket is transferred by a chain drive to a second sprocket attached to a drive shaft acting within a drive tube located at the perimeter of the spool. The drive shaft is connected to the primary drive shaft through a set of bevel gears housed in the drive tube and which drive tube is insulated and ventilated to maintain ambient room conditions within the drive tube at all times. In one configuration the drive tube is located at the periphery of the spool and contains one spindle for one mold. In another configuration the drive tube is located at the spool center aligned with the axis of the spool and containing two opposing spindles to drive two molds simultaneously.
A yet further object of the present invention is to provide a rotational molding oven wherein the drive means for the secondary axis drives a chain through an idler sprocket to the perimeter of spool where the chain engages drive pins and effects control over the rotational motion of the spool and wherein the drive can be stopped, started and reversed at will to alter the nature of the molding process.
An even further object of the present invention is to provide a rotational molding oven wherein a drive means for a cooling fan is located on top of the oven driving a sprocket acting at the center of the secondary axis, which rotational motion is transferred to a second sprocket connected by a chain to a sprocket attached to a drive shaft which acts through a drive tube located at the perimeter of the spool. The drive shaft is connected to a cooling fan located within the insulated drive tube and which fan maintains the conditions within the drive tube close to the ambient room temperatures. In another configuration the fan and drive shaft are located at the spool center aligned with the axis of the spool.
A still further object of the present invention is to provide a rotational molding oven supporting a mold at the center and rotating the mold in center-less fashion about two axes of rotation at the center of the oven wherein the oven will be least possible size to house the rotating mold.
Another object of the present invention is to provide a rotational molding oven that is simple and easy to package, transport, install and use.
A still further object of the present invention is to provide a rotational molding oven that is economical in cost to manufacture.
Additional objects of the present invention will appear as the description proceeds.
A rotational molding oven for forming an object from a mold filled with resin is disclosed by the present invention. The rotational molding oven includes a cavity for retaining the mold, a burner for heating the cavity and melting the resin, fans for cooling the cavity and hardening the resin, a device for rotating the mold about two axes, a drive means for each direction of rotation which is mounted on the exterior of the oven wherein the secondary axis of rotation is driven in either direction and the primary axis of rotation is directly driven, and wherein the secondary rotation can be reliably and accurately started, stopped and reversed as required to optimize the resin distribution within the mold during molding.
To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated and described within the scope of the appended claims.